The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
In many automatic transmissions, hydraulic piston and cylinder assemblies engage and disengage clutches to achieve a desired power flow path corresponding to a desired gear ratio or speed, typically in a sequence of gear ratios or speeds. Such operation occurs in both clutch-to-clutch (multiple planetary) and dual clutch (DCT) transmissions.
In such transmissions, the smoothness and overall quality of a shift is primarily determined by the characteristics of clutch engagement, for example, how quickly clutch engagement begins after a clutch engagement command and how rapidly the clutch engages. Such clutch engagement characteristics are, in turn, the product of hydraulic fluid application, that is, the pressure of fluid application, the volume of fluid application and the duration and time based function of these application characteristics.
In these transmissions, it is often desirable to know the status of hydraulic clutches, especially as filling nears completion when the hydraulic pressure on the clutch can be controlled to achieve controlled and optimum clutch engagement.
In such transmissions, if clutch pressure control is begun when the hydraulic chamber of the clutch is not fully filled with transmission oil, it may result in engine flare when the engine speed rises suddenly due to lack of load. Similarly, when the clutch fill phase is extended for longer than necessary, sudden, uncontrolled engagement of the clutch may result and cause a bumpy gear shift or a transmission tie-up. Hence, it is important to monitor clutch fill pressure and fill the clutch chamber exactly as appropriate and than continue to the next phase to maintain shift quality and increase reliability on clutch materials.
The present invention is directed to a method of detecting substantial filling of a hydraulic cylinder of a hydraulically operated clutch of a vehicular automatic transmission.